1. Field of the Invention
This invention relates to supermolecular structures that are used to build semi-conductor devices. More specifically, this invention relates to structures and devices based on the controlled discrete distribution and arrangement of single impurity dopant atoms or molecules within a lattice or amorphous matrix. The controlled arrangement of dopants in a semiconductor matrix provides structures that exhibit very beneficial characteristics by engineering single-charge effects. The invention also relates to methods of manufacturing such structures and devices.
2. Description of the Problem
There exists a need for the ability to control and order the distribution and effect of impurities, eg. dopant atoms, in a lattice or semiconductor matrix. Such an ability would open new opportunities to making xe2x80x98smartxe2x80x99 nanoelectronic structures. Today""s semiconductor based microelectronics relies on device structures with stochastic distributions of dopants. Conventional doping is treated as a macroscopic phenomenon, as it adds large numbers of atoms to semiconductor materials. It would be advantageous to develop structures that represented the ultimate limits of doping and host material control.
For large numbers of atoms, the typical behavior and distribution of these atoms is governed by Boltzman or Fermi-Dirac statistics. From this stochastic perspective, doping effects a shift of Fermi level states. These states are dependent on temperature, dopant concentration, and semiconductor band gap. FIG. 1 illustrates pn-junction barrier height as a function of band gap and Fermi level position. The Fermi level position corresponds to a dopant concentration. In this macroscopic case, the addition or subtraction of one to a few extra dopant atoms or electrons to the system does not induce a significant change to the potential distribution. In FIG. 1, NB is the potential barrier height in a pn-junction, Eg is semiconductor band gap, EFd and EFa are Fermi levels in respectively acceptor-doped and donor-doped parts of semiconductor, Na, Nd are volume concentrations of acceptors and donors, respectively, such that, NB=Egxe2x88x92(EFn+EFp). For a complete discussion of doping effects, see the book by S. M. Sze, Physics of Semiconductor Devices, (1981, Johne Whiley and Sons, Inc.), which is incorporated herein by reference.
Conventional scaling of semiconductor devices to smaller and smaller sizes fundamentally will become limited by the macroscopic behavior described above. As devices become smaller and smaller, the numbers of dopant atoms in a device or region of interest also continues to decrease. At some point, the number of dopants in the active areas become so small that performance will be dominated by small number effects and will no longer be controlled sufficiently by the stochastic distributions of dopants. Using conventional semiconductor manufacturing methods in this small number domain, the properties of the device become unpredictable and uncontrollable. It would be desirable to tightly control the distribution atoms in a material by atomic level engineering, such that the behavior of the material can be predicted by leveraging single charge effects.
The present invention solves the above-described problem by providing materials and devices based on the creation of a supermolecular, semiconducting structure. This structure results from the controlled discrete distribution of, and arrangement of, single-impurity atoms or molecules within a host matrix, rather than on a stochastic distribution of dopants in a continuum or lattice environment. The general principle of operation is based on single charge effects, when considerable change in the potential in a system occurs due to addition, or modification, of a single charge.
The invention provides a supermolecular structure made up of a host material with controlled impurities. The positions of the component atoms in the structure are fixed and controlled to impart predictable properties to the structure. The structure can be described by the empirical formula HAxcexa3Xia where H defines the host material, A is a number representing the number of host atoms in the structure, X defines the ith impurity, and a defines the quantity of the ith impurity. The structure defined by this formula can be used to form a pn junction or a bipolar cell.
With the present invention, a single-dopant pn junction is created by depositing a single donor atom so that it resides at a first side of a host structure, and depositing a single acceptor atom at a second, opposing side. The single donor and acceptor atoms are positioned so that a single dipole is created within the host structure. A pn junction device can be made from a cell as described here by building the structure on a substrate and attaching contact electrodes.
As mentioned above, the invention also facilitates creation of a single-dopant bipolar cell. To form this bipolar cell, a pair of atoms, both either donor or acceptor atoms, resides at opposing sides of the host structure the atoms of the pair. If the atoms in the pair are donors, the single atom is an acceptor. If the pair of atoms are acceptors, the single atom is a donor. The atoms are all positioned so that two asymmetrical potential wells, separated by a barrier, are formed within the semiconductor. The bipolar cell can be made into a stand-alone device by adding an insulating substrate and contact electrodes. This device can either function as a bistable device or an oscillator, depending on operating temperature, as will be discussed later.
The present invention also can be used to create an oscillator array from a plurality of electrostatically coupled bipolar cells. This array can be used to make a semi-conductor oscillator since the array provides a means of generating coherent oscillations that will result if the array is maintained at a temperature equal to or greater than a threshold temperature. An oscillator device is made from the array built on an insulating substrate. Contact electrodes are connected to the array as a means of connecting the device to external circuitry, and a thermal energy supply system is included to maintain the proper operating temperature of the array. Oscillator arrays and/or oscillator devices as described above can be used to make energy converters, seemingly self-powered electrical devices, wireless interconnects, and a myriad of other devices.
Single-dopant cells according to the invention may be fabricated either horizontally or vertically. In the horizontal case, a single, three-atom set of dopants is placed on a semiconductor substrate. An epitaxial film of the semiconductor is grown over the three-atom set, and at least one, but usually several, insulating monolayers are passivated. Placing several three-atom sets of dopant atoms onto the substrate in the first step can make a plurality of horizontal cells. A pattern, which defines the shape of the cells, is produced at the surface of the epitaxial film.
In the vertical case, the three-atom set is formed vertically by placing a first atom of a first type on the substrate, growing a first epitaxial layer, placing a single atom of a second type on the first epitaxial layer and growing another epitaxiai layer, and so on. The cell is again passivated at the end of the process. A plurality of vertical cells is fabricated by placing multiple first atoms of the first type, multiple single atoms of the second type, and multiple second atoms of the first type to form multiple, vertical three-atom sets. In the multiple cell fabrication process, patterns defining the shapes of the cells are produced at the top epitaxial layer.